1. Field of the Invention
The present invention relates to an aluminum based alloy having excellent mechanical properties at up to about 300.degree. C.
2. Description of Background Art
Aluminum and aluminum alloys have a combination of good mechanical properties and low density that make them useful for some aerospace applications. However, most prior aluminum alloys have had a maximum use temperature of about 150.degree. C.
Prior attempts to improve the high temperature mechanical properties of aluminum alloys have included the addition of inert particles such as alumina into an aluminum matrix. The inert particles strengthen the alloy and help it to maintain properties at elevated temperatures. However, the benefits obtained in the addition of such particles are limited and such materials have not found widespread application.
Other attempts to improve the mechanical properties of aluminum have focused on the development of stable intermetallic particles in an aluminum matrix by rapid solidification. U.S. Pat. No. 4,647,321 is typical of such alloys. This type of alloy has generally been observed to undergo particle coarsening and resultant loss of mechanical properties during processing.
A limited number of alloys are known which contain the element scandium. One group of such alloys is typified by U.S. Pat. Nos. 4,689,090 and 4,874,440, in which scandium is described as promoting or enhancing superplasticity. Superplasticity is a condition wherein, at elevated temperatures, a material displays unusual amounts of ductility and can be readily formed into complex shapes. Superplasticity is generally regarded as incompatible with elevated temperature strength and stability.
Another patent WO 95/32074 suggests the use of scandium to enhance the weldability of aluminum alloys. Finally, U.S. Pat. No. 5,620,652 mentions the possible small amounts of scandium as grain refinement agents.
Other patents relating to scandium containing aluminum alloys include WO 96/10099.
None of these prior patents appear to suggest the use of scandium in an aluminum alloy for use at elevated temperatures.